What Is a Cold-blooded Animal?
Many animals such as fish, frogs, snakes and lizards are often called “cold-blooded,” as opposed to “warm-blooded” mammals and birds. This does not mean their blood is always cold.
Unlike warm-blooded animals, they do not have built-in temperature controls that keep their bodies evenly warmed. Instead, their body temperature is usually near that of the surrounding air or water.
The cold-blooded animal is hot in hot weather, and cold in cold weather. Many depend on the sun for their body heat. Lizards, for example, bask in the sun to warm their bodies.
While basking, reptiles will lie perpendicular to the direction of the sun to maximize the amount of sunlight falling on their skin. They will also expand their rib cage to increase their surface area and will darken their skin to absorb more heat.
When a reptile is too hot, it will lie parallel to the sun’s rays, go into a shady area, open its mouth wide, lighten its skin color or burrow into cool soil.
Cold-blooded animals are much more active in warm environments and are very sluggish in cold environments. This is because their muscle activity depends on chemical reactions which run quickly when it is hot and slowly when it is cold.
A cold-blooded animal can convert much more of its food into body mass compared with a warm-blooded animal.